The present invention relates to a method of producing thin film patterns on a glass substrate.
Photolithography is a well-known technique for producing patterns in thin films formed on substrates. This technique is convenient and advantageous, having regard to the desirability of removing portions of the thin film to be processed without causing damage to the underlying surface. However, a somewhat large number of steps is necessary for completing patterning procedure in accordance with this method. Namely, after forming the thin film to be treated on a substrate, a photoresist film is formed and patterned; the thin film is subjected to an etchant through the patterned photoresist film as a mask and then the photoresist film is removed.
Laser scribing techniques are well known in the art as a low cost patterning method capable of carrying out the scribing at a high speed. YAG laser (IR light, 1.06 microns) is a representative laser which has been generally used for this purpose. Since the optical energy of this laser is only 1.23 eV, however, tin oxide, indium oxide (or ITO), ZnO or so forth having optical energy gaps of about 3 to 4 eV are not effectively processed by the YAG laser. While transparent conductive oxide (CTO) films are generally made of this class.
This laser scribing method has another shortcoming. When portions of a transparent conductive film formed over a soda-lime glass substrate with an ion blocking film therebetween is removed in order to produce electrode patterns thereon, the ion blocking film and the glass substrate are partially eliminated together, and therefore the surface of the glass substrate is exposed. Eventually, in case of liquid crystal device manufacture, the liquid crystal material contained in the device is contaminated by sodium ions introduced from the glass substrate. Furthermore, the scribing makes the upper surface thereof uneven as well as residue remaining on the edges of the removal portions, the residue is piled as high as 0.5 to 1 micron. The unevenness is undesirable not only in regard to the application to liquid crystal devices but also to the manufacture of general electric devices including laminating process. The uneven surface might may be the cause of electrical shorting between different levels of the laminate and disconnection of the electrical patterns superimposed thereon.